Computer users are accustomed to using a mouse and keyboard as a way of interacting with a personal computer. While personal computers provide a number of advantages over written documents, most users continue to perform certain functions using printed paper. Some of these functions include reading and annotating written documents. In the case of annotations, the printed document assumes a greater significance because of the annotations placed on it by the user. One of the difficulties, however, with having a printed document with annotations is the later need to have the annotations entered back into the electronic form of the document. This requires the original user or another user to wade through the annotations and enter them into a personal computer. In some cases, a user will scan in the annotations and the original text, thereby creating a new document. These multiple steps make the interaction between the printed document and the electronic version of the document difficult to handle on a repeated basis. Further, scanned-in images are frequently non-modifiable. There may be no way to separate the annotations from the original text. This makes using the annotations difficult. Accordingly, an improved way of handling annotations is needed.
One technique of capturing handwritten information is by using a pen whose location may be determined during writing. One pen that provides this capability is the Anoto pen by Anoto Inc. This pen functions by using a camera to capture an image of paper encoded with a predefined pattern. An example of the image pattern is shown in FIG. 21. This pattern is used by the Anoto pen (by Anoto Inc.) to determine a location of a pen on a piece of paper. However, it is unclear how efficient the determination of the location is with the system used by the Anoto pen. To provide efficient determination of the location of the captured image, a system is needed that provides efficient decoding of the captured image.
When annotating a document, a user may mark the document by moving a pen tip with respect to the document. The path of the pen tip may comprise a plurality of strokes, where each stroke corresponds to a series of captured images. Hence, efficiently identifying the path of the pen in order to process the annotation on a document would be desirable.
Portions of the positionally encoded information, such as a watermarked maze pattern, may be occluded by the document's content, such as text and/or graphics. When a document's content occludes a relatively small amount (or none) of the position-encoding information in an area of a document, then the area's location within the document can be determined efficiently without a need to perform costly computations to determine the location. When the document's content occludes a relatively large amount of the position-encoding information in an area of the document, however, more computationally intensive techniques may need to be used to determine the area's location within the document. Accordingly, techniques for distinguishing cases in which a relatively small amount of the position-encoding information is occluded from cases in which a relatively large amount is occluded would be desirable to increase the efficiency with which users are able to interact with documents containing positionally encoded information.